The invention relates to collecting ionizing radiation, in particular radiation emitted by radioactive biological markers, and to converting the radiation into light signals for use by apparatus for detecting ionizing radiation.
This type of apparatus is commonly used in the medical field to locate the radioactive nuclei of (marker) molecules injected into the human body prior to surgery. One such apparatus is described in particular in European patent EP 0 650 601.
The invention relates more particularly to collection devices comprising a scintillating element housed in a sheath that is opaque to light and that has a first end arranged to receive ionizing radiation and a second end delivering light signals derived from conversion of the ionizing radiation received by the first end.
In document EP 0 650 601, the opaque sheath and the scintillating element which is a scintillating fiber are directly connected to the detector apparatus, thus requiring scintillating fibers that are several meters long. In document U.S. Pat. No. 4,788,436, the second end of the scintillating element (which is likewise a scintillating fiber) is stuck to the first end of an optical fiber whose second end is for connection to a detector apparatus to deliver thereto the light signals produced by the scintillating fiber. Consequently, the sheath extends from the first end of the scintillating fiber to the second end of the optical fiber and, as a result, it holds both the scintillating and the optical fibers captive on a permanent basis. Failure of either one of the fibers thus requires the entire collection device to be replaced.
An object of the invention is to improve the situation by providing a solution different from known solutions.
To this end, the invention provides a device for collecting ionizing radiation, the device comprising a scintillating element housed in an opaque sheath, filter means placed at the first end of the sheath to prevent at least external photons (xcexd) gaining access to the first end of the scintillating element, and first connection means at the second end of the scintillating element and suitable for connection to light guide means to enable said second end of the scintillating element to be coupled to the end of a light guide of said light guide means.
As a result, the collection device is an active element which is reversibly connectable to a passive light guide element (the two elements together forming a collection assembly), such that it can be replaced independently of the passive element, and its dimensions may be selected as a function of applications. In addition, since the device is not subject to interference from photons, it presents a signal/noise ratio that is considerably better than that of prior art devices, and as a result it improves the sensitivity of the detection apparatuses to which it can be connected via a passive light guide element.
Advantageously, the length of the scintillating element lies in the range about 0.1 millimeters (mm) to about 1 meter (m), and more preferably in the range about 0.1 mm and about 50 centimeters (cm), and still more preferably in the range about 0.1 mm to about 5 cm.
The connection between the active device and the passive light guide element may be provided in various ways, in particular by means of a coupling element that is preferably made of a material presenting a refractive index that is substantially equal to that of glass.
In a first embodiment, the second end of the opaque sheath extends beyond the second end of the scintillating element, to form an extension of selected length which is deformed to make the first connection means. Under such circumstances, the deformation enables at least one end of the light guide to be inserted inside the opaque sheath. The first connection means is thus in the form of a sleeve.
In a second embodiment, the first connection means is a separate part having first retention means, for example snap-fastening means or a thread for co-operating with complementary retention means formed on the second connection means of the light guide means.
The filter means are preferably made in the form of an endpiece comprising a first material in sheet form presenting weight lying in the range approximately 40 grams per square meter (g/m2) to about 300 g/m2, and in particular black paper. The endpiece may also comprise a second material in sheet form serving to block ionizing radiation of the gamma ray (xcex3) type, e.g. mylar type polyethylene terephthalate (PET) and secured to the first material in sheet form by an intermediate bonding layer, e.g. an adhesive that is transparent to ionizing radiation, such that only beta type (xcex2) ionizing radiation is converted.
The scintillating element may be selected from a group comprising one or more scintillating optical fibers, scintillating grains, scintillating crystals such as CsI, NaI, and BGO, a scintillating plastics material of weight preferably lying in the range about 0.8 milligrams per square centimeter (mg/cm2) to 1.6 mg/cm2, a scintillating liquid, and a scintillating gel.
When the scintillating element is made up of a plurality of substantially identical scintillating fibers, it is advantageous for them to form a bundle and to be coupled to a light guide bundle of the light guide means. Under such circumstances, it can be advantageous for the filter means to comprise a zone selected to be of small extent that allows xcex3 type and xcex2 type ionizing radiation to enter, such that the scintillating fiber can convert the received xcex3 and xcex2 ionizing radiation into light signals.
In another embodiment, the scintillating element comprises a first portion placed downstream of the filter means to convert xcex3 ionizing radiation into photons, and a second portion placed downstream of said first portion for converting xcex2 type ionizing radiation into photons. Under such circumstances, it is particularly advantageous for the first portion to be constituted by scintillating crystals selected from the group comprising at least CsI, NaI, and BGO, and for the second portion to be a scintillating plastics material of weight lying preferably in the range about 0.8 mg/cm2 to 1.6 mg/cm2.
The invention also provides an ionizing radiation collection assembly comprising light guide means suitable for being connected to a collection device of the type specified above.